Inductor for inductive h. f. heating



Oct. 2, 1956 D. C. VAN IPEREN INDUCTOR FOR INDUCTIVE H.F. HEATING Filed Dec. 30, 1953 INVENTOR DIRK CHRISTIAAN VAN IPEREN W54 M'WK AGENT United States Patent Ofiice 2,765,389 Patented Oct. 2, 1956 INDUCTOR FOR INDUCTIVE H. F. HEATING Dirk Christiana van Iperen, Eindhoven, Netherlands, as-

signor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application December 30, 1953, Serial No. 401,325

Claims priority, application Netherlands January 10, 1953 7 Claims. (Cl. 219-1019) This .invention relates to an inductor for inductive HF-heating comprising conductors for connection to a, high-frequency generator. If a work-piece is to be heated only at one comparatively narrow area and if use is made of an inductor of the usual type which consists of only one Winding, the work-piece is arranged in the vicinity of one conductor in such manner that the surface of the work-piece is at right angles to the plane passing through the winding. However, this involves the loss of a considerable part of the electro-magnetic field which is generated by the winding and which is not closed through the work-piece, while the coupling factor between workpiece and inductor is low. If one would obviate the said disadvantage by providing the work-piece at a short distance from the surface of the winding and in parallel therewith, two heating paths generally occur. If the winding is made so narrow that the two said paths are coincident, the winding has a low inductance, so that the inductor takes up a comparatively high power in the unloaded state, which is likewise disadvantageous.

In order to mitigate the said disadvantages the inductor according to the invention is constituted by a hollow body which preferably comprises a core of material having low high-frequency losses and which exhibits an aperture, one connecting conductor being provided in the vicinity of the edge of the aperture and the other being connected at the opposite side of the aperture likewise in the vicinity of the edge and thence extending at themost at a small distance from the plane through the aperture between the lateral edges thereof until in the vicinity of the first-mentioned connecting conductor.

In an inductor of this shape the apertures which exhibit between the lateral edges of the hollow body and the last-mentioned connecting conductor serve as the working aperture. This affords the advantage that the work-piece may be heated at only one comparatively narrow area, that the inductance of the inductor in the unloaded state has a reasonable high value, so that the no-load current is low, and that the field of the lines of force surrounding the hollow body which serves as a conductor contributes to the heating. It is important that the coupling factor between work-piece and inductor should be high, so that the working power is high. The inductor according to the invention is suited more particularly for superficial hardening.

In order that the invention may be readily carried into effect, it will now be described with reference to the accompanying drawing showing diagrammatically, by way of example, some embodiments thereof.

Fig. 1 is a sectional view of a known rectangular inductor.

Fig. 2 is a sectional view of a known rectangular inductor, .if only one heating area is desired.

Fig. 3 shows the inductor according to the invention.

Fig. 4 .is a cross-sectional view at right angles to the longitudinal direction of conductor 8 of Fig. 3.

Figs. 5, 6 and 7 show some other practical forms of the invention.

Fig. 8 shows the connecting conductor 5 as a conduit through which a cooling liquid flows.

Fig. 9 is an embodiment in which the connecting conductor 8 is also a conduit through which a cooling liquid flows.

Fig. l is a sectional view of a known rectangular inductor 1, a work-piece 2 being arranged in parallel with the plane through the inductor at a short distance therefrom. The field of the lines of force surrounding the two conductors is designated 3. As a rule, the workpiece 2 will in this case be heated at the two areas indicated by 4. If only one heating area is desired, the conductors 1 would have to be approached very closely, so that the two areas 4 are coincident. This results in a material decrease in the inductance of the inductor in the unloaded state, so that the no-load current is high. If a reasonable no-loa-d current and heating at one area is desired, it is necessary to utilize an inductor having a comparatively high inductance and hence a large surface of the coil and to provide the surface of the work-piece at right angles to the plane passing through the inductor, as shown in Fig. 2. This results in heating of the area 4 only, but the lines of force 3 surrounding the upper conductor 1 do not participate in the heating and thus are a loss.

The inductor according to the invention is shown in Fig. 3. A connecting conductor 5 is connected to the edge of an aperture 6 of a hollow body 7, and another connecting conductor 8 being connected, at the opposite side, to the edge of the aperture 6 and thence extending at a small distance from the plane through the aperture 6 until in the vicinity of the conductor 5. The working aperture exists between lateral edges 9 and the conductor 8. Fig. 4 is a cross-sectional view at right angles to the longitudinal direction of conductor 3, the work-piece here being indicated by 10, the direction of movement by an arrow and the heated zone by 11.

The fields of the lines of force surrounding the conductor 8 and the hollow body 7 are designated 12 and 13 respectively. Due to the particular shape of the hollow body 7, the field 13 is forced towards the work-piece 110, thus assisting in the heating of the work-piece in the vicinity of the boundaries of the heated zone 11. Furthermore, the inductance of the inductor in the unloaded state is sufficiently high and the coupling factor is favourable. It is evident that for a given work-piece the size and the shape of the inductor are required to be matched thereto according to the heating requirements (size of the zone to be heated, temperature, material) and the desired inductance with no-load.

Some other practicable forms are shown in section in Figs. 5, 6 and 7. In these figures the working aperture is made even smaller, so that the lines of force surrounding the hollow body are deflected still further towards the heating area. However, it has been found that the working aperture cannot be chosen unduly narrow, since otherwise the current flowing through the hollow body will not be distributed more or less evenly throughout the section thereof, but flows substantially along the two edges 9, resulting fundamentally in an approximation of the narrow coil and a decrease in inductance when the inductor is not loaded.

In Fig. 6 the hollow body comprises a core 14, for example of ferrite material, the core projecting above the hollow body, so that the material of the core is also present between the connecting conductor 8 and the edges 9 of the hollow body. This results in the inductance of the inductor being increased and the concentrated field being brought as closely as possible to the zone to be heated.

The inductor shown in Fig. 7, in addition to being cylindrical, may also be spherical in shape.

In Fig. 8, the connecting conductor 5 is constituted by a conduit through which cooling liquid flows into the hollow body 7 which thus serves itself as a container. The cooling liquid may serve to cool the core, if available, of the inductor, as well as to chill the heated portion of the work-piece during the movement thereof (see the arrow in Fig. 4).

Another embodiment is shown in Fig. 9 in which the' connecting conductor 8 is also constituted by a conduit which serves for the discharge of cooling liquid. The cooling liquid is here evenly distributed through the inductor and the core (if present) through small apertures 15.

The hollow body may have secured to it small rollers for supporting the workpiece at the correct distance above the conductor 8 and for obtaining an easy movement thereof above the inductor.

The inductor may alternatively be used in the inversed position, so that the work-piece is provided under the inductor and is chilled more intensely by the cooling liquid flowing down.

What is claimed is:

1. An inductor for inductive HF heating comprising a plurality of substantially flat conductors for connection to a high frequency generator, said inductor being closed on all said sides with the exception of said top portion which is provided with an aperture, one of said conductors being connected to said inductor at the peripheral edge of said inductor aperture, and another conductor. being connected to said inductor at an opposite edge of said inductor aperture, said other conductor extending in a different plane from said one conductor and having part thereof adjacent to the latter.

2. An inductor as set forth in claim 1 further comprising an inductor winding, and the surface of the working aperture of said inductor being smaller than the crosssectional surface of said inductor winding.

3. An inductor as set forth in claim 1 wherein at least one of said conductors is a channel for the supply of cooling agent which communicates with said inductor so that the latter serves as a container for said cooling agent.

4. An inductor as set forth in claim 1 wherein the two conductors are channels for the supply of cooling agent, the part of said conductors being in said inductor being provided with a plurality of openings therein.

5. An inductor as set forth in claim 1 wherein the other conductor is located in a plane above the plane of said apertured inductor.

6. An inductor as set forth inclaim 1 further comprising a core material of low high-frequency losses in said inductor wherein said core material projects above the peripheral edge of said inductor aperture.

7. An inductor as set forth in claim 1 wherein said inductor is rectangular shaped and provided with a completely open top surface.

References Cited in the file of this patent UNITED STATES PATENTS 2,477,029 Wood July 26, 1949 2,606,997 Beckius et al. Aug. 12, 1952 2,673,922 Edwards Mar. 30, 1954 FOREIGN PATENTS 383,859 Great Britain Nov. 24, 1932 

